/* ============================================================
   天道篇终章 · 终极三问 · 「下潜竖井」入口
   用在：tiandao.html（总览页末）· tiandao-emptiness.html（空性篇末）
   形态刻意区别于法则卡——一道向下的渊井，预告沉浸式下潜体验。
   呼应 问渊 页配色：violet → abyss 渐深 + gold 中脉。
   ============================================================ */
.capstone-gate{
  display:block; position:relative; overflow:hidden;
  max-width:760px; margin:88px auto 0; padding:50px 30px 54px;
  text-align:center; text-decoration:none; color:var(--ink);
  background:linear-gradient(180deg,
    rgba(109,92,160,.12) 0%,
    rgba(45,36,70,.34) 52%,
    rgba(13,11,20,.66) 100%);
  border:1px solid rgba(200,150,74,.22);
  transition:border-color .45s ease, transform .45s ease, box-shadow .45s ease;
}
.capstone-gate::before{                 /* 中脉 / 井绳 */
  content:""; position:absolute; left:50%; top:0; bottom:0; width:1px;
  transform:translateX(-50%);
  background:linear-gradient(180deg, rgba(232,201,143,.65), rgba(200,150,74,.14) 68%, transparent);
  opacity:.5; pointer-events:none;
}
.capstone-gate:hover{
  border-color:rgba(232,201,143,.5);
  box-shadow:0 18px 60px -30px rgba(109,92,160,.6);
  transform:translateY(-2px);
}
.capstone-k{
  position:relative; font-family:var(--mono); font-size:10px;
  letter-spacing:.34em; text-transform:uppercase; color:var(--gold);
}
.capstone-t{
  position:relative; display:block; margin-top:16px;
  font-family:var(--serif-cn); font-weight:500;
  font-size:clamp(30px,6vw,46px); letter-spacing:.18em; color:#f3ead4;
}
.capstone-q{
  position:relative; display:block; margin-top:15px;
  font-family:var(--serif-cn); font-size:15px; letter-spacing:.12em;
  color:var(--ink); opacity:.84;
}
.capstone-d{
  position:relative; display:block; margin-top:10px;
  font-family:var(--serif-cn); font-size:13px; line-height:1.7; color:var(--ink-dim);
}
.capstone-go{
  position:relative; display:block; margin-top:26px;
  font-family:var(--serif-en); font-size:24px; color:var(--gold-bright);
  animation:capDescend 3.2s ease-in-out infinite;
}
@keyframes capDescend{
  0%,100%{ transform:translateY(0); opacity:.5; }
  50%    { transform:translateY(8px); opacity:1; }
}
@media (max-width:640px){
  .capstone-gate{ margin-top:64px; padding:40px 18px 44px; }
}
@media (prefers-reduced-motion:reduce){
  .capstone-go{ animation:none; opacity:.85; }
}